Buck converter based on LMR33620ADDAR lower voltage output.

Thread Starter

cipek

Joined Oct 24, 2023
1
Hi all,
I've used LMR33620ADDAR buck converter in my project. TI Webench to design the circuit of that converter, but it doesn't work as expected. I'm not sure whether my layout is bad or some of the components are incorrect or both. When I disconnect U5, and apply 3.3V directly the MCU works and all the levels are correct. The U4 has an output of around 3V instead of 12V. I would appreciate if you could have a look at the pics.
BOM:
Farnell
U4LMR33620ADDA3007263
C1710uF2211159
C18220nF2905327
C191uF2522376
C22100nF2611911
C23, C24, C25, C2722nF2581029
C28100uF1539477
L222uH1869771
R16, R17100k2826073
R189.09k1160198
C32,C33100uF1539477
U5LM1117MPX-3_3_NOPB3122024


1704738995550.png 1704739058894.png
1704740062903.png
Based on Webench:
1704740916463.png
 

Ian0

Joined Aug 7, 2020
9,792
I use an LMR38010, which might be a close relative of the LMR33620. When it was happy it worked beautifully, but it was really picky about the decoupling of its power input. It needed 1uF right on the power pin, 25mm away wasn't good enough for it.
Your supply decoupling actually looks OK, but I can't see where all the grounds go.
Does it behave peculiarly in different ways as you vary the input voltage? That's what my LMR38010 did!
 
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